1. Field of the Invention
The present invention relates to an apparatus for controlling a starting clutch of a vehicle having a function of stopping engine idling so that an engine is automatically stopped under given conditions when the vehicle is at a standstill, the starting clutch being provided in a transmission of the vehicle in series with a belt type continuously variable transmission mechanism.
2. Description of Related Art
In case a transmission is constituted such that a power of an engine is inputted into a belt type continuously variable transmission through a power transmission mechanism such as a forward/reverse switching mechanism or the like which has built therein hydraulically operated engaging elements, the following may happen. Namely, in a vehicle in which the engine idling is stopped when the vehicle is at a standstill, at the time of vehicle start-up from the state of engine stopping, the hydraulic oil pressure in a hydraulic circuit becomes zero while the engine is stopped and, consequently, the power transmission mechanism becomes an out-gear state (a state not fit for power transmission). Therefore, if a starting clutch is engaged earlier, the power is suddenly transmitted to driving wheels of the vehicle when the power transmission mechanism has become an in-gear state (a state of being geared in) in which the power transmission mechanism transmits power, resulting in shocks.
In order to eliminate such disadvantages, the following is considered. Namely, at the time of vehicle start-up from the state of engine stopping, the control mode of the starting clutch is switched, when the power transmission mechanism has become an in-gear state in which the power is transmitted, from a waiting mode in which the engaging force of the starting clutch is kept below a creeping force which generates the creeping of the vehicle to a running mode in which the engaging force of the starting clutch increases above the creeping force.
To a drive pulley and a driven pulley of the belt type continuously variable transmission mechanism, there is applied a pulley side-pressure by means of a cylinder which is provided on each of the pulleys. At the time of vehicle start-up from the state of engine stopping, even if the power transmission mechanism becomes the in-gear state, the cylinder will not be completely filled with hydraulic oil. As a result, the cylinder side-pressure sometimes will not rise. If the engaging force of the starting clutch increases above the creeping force before the pulley side-pressure rises, the load to be operated on the continuously variable transmission mechanism increases. Consequently, a slip occurs between the belt and the pulleys of the continuously variable transmission mechanism. Even if the pulley side-pressure has risen, it takes time for the pulley side-pressure to reach a sufficiently high pressure. During such a time, if the control mode of the starting clutch is switched to the running mode and the engaging force of the starting clutch rapidly increases, the pulley side-pressure becomes insufficient relative to the load torque to be operated on the continuously variable transmission mechanism. As a result, slipping occurs between the belt and the pulleys of the continuously variable transmission mechanism. If this kind of slipping occurs, the durability of the belt is adversely affected.
In view of the above points, the present invention has an object of providing an apparatus for controlling a starting clutch of a vehicle having a function of stopping engine idling so that an engine is automatically stopped, wherein belt slipping is prevented at the time of vehicle start-up from the state of engine stopping.
In order to attain the above and other objects, according to a first aspect of the present invention, there is provided an apparatus for controlling a starting clutch of a vehicle having a function of stopping engine idling so that an engine is automatically stopped under given conditions when the vehicle is at a standstill. The starting clutch is provided in a transmission of the vehicle in series with a belt type continuously variable transmission mechanism. The apparatus comprises: engagement preventing means for preventing an engaging force of the starting clutch from increasing above a creeping force which gives rise to creeping of the vehicle, the preventing being made at a time of vehicle start-up from the state of engine stopping until after a lapse of a predetermined time.
According to a second aspect of the present invention, there is provided an apparatus for controlling a starting clutch of a vehicle having a function of stopping engine idling so that an engine is automatically stopped under given conditions when the vehicle is at a standstill. The starting clutch is provided in a transmission of the vehicle in series with a belt type continuously variable transmission mechanism. The apparatus comprises: increase limiting means for limiting a speed of increase in an engaging force of the starting clutch. The limiting is made, until after a lapse of a predetermined time in a step in which the engaging force is increased above a creeping force which gives rise to creeping of the vehicle at a time of vehicle start-up from a state of engine stopping, by keeping an upper limit value of the speed of increase in the engaging force below a value after the lapse of the predetermined time.
According to a third aspect of the present invention, there is provided an apparatus for controlling a starting clutch of a vehicle having a function of stopping engine idling so that an engine is automatically stopped under given conditions when the vehicle is at a standstill. The starting clutch is provided in a transmission of the vehicle in series with a belt type continuously variable transmission mechanism which receives an input of a power from the engine through power transmission mechanism having built therein hydraulically operated frictional engaging elements, wherein, at a time of vehicle start-up from a state of engine stopping, a control mode of the starting clutch is switched from a waiting mode in which an engaging force of the starting clutch is kept below a creeping force which gives rise to creeping of the vehicle to a running mode in which the engaging force of the starting clutch is increased above the creeping force. The switching is made at a time when the power transmission mechanism has become an in-gear state in which the power is transmitted. The apparatus comprises increase limiting means for limiting a speed of increase in the engaging force. The limiting is made, until after a lapse of a predetermined time from a point of time of switching to the running mode, by keeping an upper limit value of the speed of increase in the engaging force below a value after the lapse of the predetermined time.
In the above-described first aspect of the present invention, if the above-described predetermined time is set to a time which is required for the pulley side-pressure of the drive pulley and the driven pulley of the continuously variable transmission mechanism to rise, the engaging force of the starting clutch will not increase above the creeping force before the pulley side-pressure rises. In this manner, the slipping in the belt of the continuously variable transmission mechanism can be prevented.
According to the above-described second and third aspects of the present invention, in the course in which the control mode of the starting clutch is switched to the running mode and in which the engaging force of the starting clutch is increased above the creeping force, the engaging force of the starting clutch is initially slowly increased. By setting the above-described predetermined time depending on the delay in the response to the increase in the pulley side-pressure, the slipping of the belt can be prevented.
In the embodiment to be described hereinafter, what corresponds to the predetermined time in the first aspect of the present invention is YTM2. What corresponds to the above-described engagement preventing means is the processing at steps S4-25 and S4-33 in FIG. 4. What corresponds to the above-described predetermined time in the above-described second and third aspects of the present invention is YTM4. The values of the upper limit value of the speed of increase after and before the lapse of the predetermined time are, respectively, Yxcex94PLMTN and Yxcex94PLMTS. What corresponds to the above-described increase limiting means is the processing at steps S25, S27, S28, S29 and S33 in FIG. 3.